S1

Supplementary Information

Oxygen-mediated Formation of MoSx-doped Hollow Carbon Dots

for Visible Light-driven Photocatalysis

Jung Hyun Park, Faizan Raza, Su-Ji Jeon, DaBin Yim, Hye-In Kim, Tae-Woog Kang, and Jong-Ho Kim*

Department of Chemical Engineering, Hanyang University, Ansan 426-791, Republic of Korea

*To whom correspondence should be addressed: kjh75@hanyang.ac.kr

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A.This journal is © The Royal Society of Chemistry 2016

S2

1. Instruments

UV/Vis absorption and photoluminescence spectra of MoSHCDs and NMP-CDs were

measured using a UV/Vis spectrometer (Mega-2100, Scinco, Korea) and a spectrofluorometer

(Nano Log®, Horiba Scientific, Japan), respectively. The structure and size of MoSHCDs and

NMP-CDs were characterized by atomic force microscope (AFM, XE-100, Park systems,

Korea) and transmission electron microscopy (TEM, JEM-2100F, JEOL, Japan). Chemical

composition of MoSHCDs and NMP-CDs were identified by x-ray photoelectron spectroscopy

(XPS, AXIS-His, KRATOS, UK). The amount of Mo doped in MoSHCDs was quantified by

inductively coupled plasma-atomic emission spectroscopy (ICP-AES, SPECTRO, SPECTRO

ARCOS, Germany), and the band edge positions of MoSHCDs were measure by cyclic

voltammetry (CV, versaSTAT4, Princeton Applied Research, USA). The products for the

oxidative coupling reaction of various amines were analyzed by gas chromatography (GC,

6500GC, YoungLin Instrument, Korea) and nuclear magnetic resonance (NMR) spectroscopy

(400 MHz, Burker model digital ADVANCE III 400).

2. Experimental Methods

A. Preparation of NMP-CDs

A 20 ml portion of pure NMP in a two-necked round bottom flask was heated up with stirring

at 140oC for 3 h under O2 or Ar atmosphere. The reaction mixture was filtered with alumina

membrane filter (20 nm), and the filtrate was concentrated under vacuum at 100oC for 6 h. The

concentrated solution was diluted with 20 mL of water, then the product (MNP-CDs) was

purified via dialysis with a membrane tube (MWCO 1,000 Da) for 1 day. NMP-CDs were

lyophilized at - 40 oC overnight.

B. Measurement of the band edge positions of MoSHCDs

S3

The Pt disk electrode and Ag wire were used as working, counter and quasi-reference

electrodes, respectively. A 20 mg portion of MoSHCDs were dispersed in 10 ml of acetonitrile

and NMP (7 : 3) mixture, followed by addition of tetrabutylammonium perchlorate (TBAP)

and ferrocene (Fc) as an electrolyte and a standard. The band edge positions of MoSHCDs were

measured by sweeping between 2.0 and -2.0 eV at the rate of 100 mV/s.

C. Quantum yield measurement

The quantum yield (QY) of MoSHCDs was measured by using Coumarin 153 solution in

ethanol (QY 0.53) as a standard. The MoSHCDs were dispersed in NMP using a probe sonicator

to measure their absorption and photoluminescence. The absorption of MoSHCDs was measured

at 400 nm, and their photoluminescence was measured under excitation at 400 nm. The

absorption remained below 0.1 to minimize a reabsorption effect.

∅𝑥 = ∅𝑆𝑇 ∙ ( 𝐺𝑟𝑎𝑑𝑥

𝐺𝑟𝑎𝑑𝑆𝑇) ∙ (

𝑛2𝑥

𝑛 2𝑆𝑇

)

= Fluorescence quantum yield∅

= The gradient from the plot of integrated fluorescence intensity vs. absorbance𝐺𝑟𝑎𝑑

= The refractive index of the solvent𝑛

The subscripts ST and X denote standard and sample, respectively.

D. Photoluminescence quenching of MoSHCDs by BA

A 2 mg portion of MoSHCDs were added into a mixture of acetonitrile and NMP (7 : 3, 10

mL), which was redispersed using a probe sonicator. To examine the quenching of MoSHCDs

photoluminescence by BA, a certain amount of benzylamine (12.4, 31, 62, and 124 mg) was

S4

added to 2 ml of MoSHCDs dispersion. After mixing for 1 min, the photoluminescence of

MoSHCDs was measured.

E. Apparent quantum yield measurement

To calculate the apparent quantum efficiency of MoSHCDs, light of 410 nm was irradiated into

the reaction solution of benzylamine using a monochrometer. External Quantum Efficiency

(EQE) was calculated using following equations (1) – (5).

𝐸𝑝 = ℎ ∙ 𝑓 = ℎ ∙ (𝑐/𝜆) (1)

𝑁𝑝 = 𝐸𝐸𝑝

(2)

𝐸𝑄𝐹 =𝑁𝑝

𝑁𝐴 (3)

𝐸𝑄𝐸 = 𝑁𝑝𝑟𝑜𝑑𝑢𝑐𝑡

𝑁𝐼𝑃 ∙ 100(%) (4)

Where is a distinct energy of photons [J], is a Planck’s constant (6.63 10-34 J·s), is a 𝐸𝑝 ℎ × 𝑐

speed of light (2.998 108 m/s), is frequency [1/s], is wavelength [m], is the number of × 𝑓 𝜆 𝑁𝑝

photons [1/ m2·s], is a power density of a light source (14.28 mW/m2), is the photon flux 𝐸 𝐸𝑄𝐹

[mol/m2·s], is the Avogadro’s number (6.02 1023/mol), is the molar amount of 𝑁𝐴 × 𝑁𝑝𝑟𝑜𝑑𝑢𝑐𝑡

product [20 mol], is the number of photons of incident light (2114.47 mol).𝑁𝐼𝑃

F. NMR analysis of various imine products

N-Benzyl-1-phenylmethanimine (N-benzylidenebenzylamine, NBBA). 1H NMR (CDCl3) :

δ (ppm) = 8.35 (s, 1H), 7.79 – 7.74 (m, 2H), 7.39 (d, J = 2.2 Hz, 3H), 7.32 (d, J = 4.4 Hz, 4H),

7.24 (s, 1H), 4.80 (d, J = 1.3 Hz, 2H); 13C NMR (101 MHz, CDCl3): δ (ppm) = 162.09, 139.40,

136.25, 130.88, 128.72, 128.61, 128.39, 128.09, 127.10, 65.16.

N-(4-Methylbenzyl)-1-(p-tolyl) methanimine. 1H NMR (CDCl3) : δ (ppm) = 8.30 (s, 1H),

7.65 (d, J = 8.4 Hz, 2H), 7.20 (d, J = 8.4, 2H), 7.18 (d, J = 8.0, 2H), 7.12 (d, J = 8.0 Hz, 2H),

4.74 (s, 2H), 2.34 (s, 3H), 2.31 (s, 3H); 13C NMR (101 MHz, CDCl3): δ (ppm) = 161.18,

S5

141.06, 136.57, 136.45, 133.70, 129.41, 129.26, 128.37, 128.07, 64.87, 21.61, 21.22.

N-(2-Methylbenzyl)-1-(o-tolyl) methanimine. 1H NMR (CDCl3) : δ (ppm) 8.63 (s, 1H),

7.92 (dd, J = 7.6, 1.4 Hz, 1H), 7.32 – 7.10 (m, 7H), 4.80 (s, 2H), 2.47 (s, 3H), 2.37 (s, 3H) 13C

NMR (101 MHz, CDCl3): δ (ppm) = 160.66, 137.84, 137.73, 136.20, 134.34, 130.93, 130.37,

130.23, 128.40, 127.84, 127.17, 126.30, 126.20, 63.41, 19.52, 19.42.

N-(4-(tert-butyl)benzyl)-1-(4-(tert-butyl)phenyl) methanimine. 1H NMR (CDCl3) : δ

(ppm) 8.35 (s, 1H), 7.73 – 7.69 (m, 2H), 7.44 – 7.40 (m, 2H), 7.37 – 7.33 (m, 2H), 7.28 – 7.23

(m, 2H),4.77 (s, 2H), 1.33 (s, 2H), 1.31 (s, 9H), 1.30 (s, 9H); 13C NMR (101 MHz, CDCl3): δ

(ppm) =161.77, 154.18, 149.87, 136.61, 133.73, 129.83, 128.23, 127.89, 127.82, 125.65,

125.50, 64.97, 35.03, 34.60, 31.56, 31.38, 31.22.

N-(4-Methoxybenzyl)-1-(4-methoxyphenyl) methanimine. 1H NMR (CDCl3) : δ (ppm)

8.26 (s, 1H), 7.72 – 7.66 (m, 2H), 7.23 (d, J = 8.8 Hz, 2H), 6.93 – 6.83 (m, 4H), 4.70 (s, 2H),

3.79 (s, 3H), 3.75 (s, 3H); 13C NMR (101 MHz, CDCl3): δ (ppm) = 161.72, 160.99, 158.70,

131.74, 129.89, 129.24, 114.03, 113.95, 64.49, 55.40, 55.33.

1-(Benzo[1,3]dioxol-5-yl)-N-(benzo[1,3]dioxol-5-ylmethyl)methanimine. 1H NMR

(CDCl3) : δ (ppm) 8.21 (s, 1H), 7.39 (d, J = 1.6 Hz, 1H), 7.11 (dd, J = 8.0, 1.6 Hz, 1H), 6.83 –

6.78 (m, 2H), 6.76 (d, J = 1.0 Hz, 2H), 5.97 (s, 2H), 5.91 (s, 2H), 4.66 (d, J = 1.1 Hz, 2H); 13C

NMR (101 MHz, CDCl3): δ (ppm) = 160.96, 150.03, 148.37, 147.84, 146.62, 133.45, 131.08,

124.67, 121.13, 108.71, 108.31, 108.13, 106.78, 101.57, 101.02, 64.61.

N-(4-Fluorobenzyl)-1-(4-fluorophenyl) methanimine. 1H NMR (CDCl3) : δ (ppm) 8.33 (s,

1H), 7.78 – 7.74 (m, 2H), 7.32 – 7.21 (m, 2H), 7.12 – 7.04 (m, 2H), 7.03 – 6.96 (m, 2H), 4.75

(s, 2H); 13C NMR (101 MHz, CDCl3): δ (ppm) = 165.65, 163.31,163.26,160.88, 160.62,

135.10, 135.07, 132.48, 132.45, 130.32, 130.32, 129.61, 129.54, 115.93, 115.72, 115.51,

115.30, 64.22.

N-(4-Chlorobenzyl)-1-(4-chlorophenyl) methanimine. 1H NMR (CDCl3) : δ (ppm) = 8.31

(s, 1H), 7.72 – 7.65 (m, 2H), 7.40 – 7.34 (m, 2H), 7.32 – 7.28 (m, 2H), 7.24 (d, J = 8.7 Hz,

2H), 4.74 (s, 2H); 13C NMR (101 MHz, CDCl3): δ (ppm) = 160.98, 137.76, 137.00, 134.58,

131.02, 129.61, 129.41, 129.07, 128.78, 64.30.

N-(2,4-Dichlorobenzyl)-1-(2,4-dichlorophenyl) methanimine. 1H NMR (CDCl3) : δ (ppm)

8.78 (s, 1H), 8.04 (d, J = 8.5 Hz, 1H), 7.41 – 7.38 (m, 2H), 7.35 (d, J = 8.3 Hz, 1H), 7.29 –

S6

7.21 (m, 2H), 4.86 (s, 2H); 13C NMR (101 MHz, CDCl3): δ (ppm) = 58.98, 137.48, 135.98,

135.47, 134.11, 133.59, 131.66, 130.60, 130.57, 130.45, 129.78, 129.47, 129.30, 128.11,

127.75, 127.37, 61.70.

1-(Pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanimine. 1H NMR (CDCl3) : δ (ppm) 8.66

(m, 1H), 8.64 – 8.54 (m, 2H), 8.09 (m, 1H), 7.79 – 7.60 (m, 2H), 7.42 (m, 1H), 7.35 – 7.28 (m,

1H), 7.24 – 7.11 (m, 1H), 5.03 (d, J = 1.4 Hz, 2H); 13C NMR (101 MHz, CDCl3): δ (ppm) =

63.87 , 158.65 , 154.29 , 149.44 , 149.30 , 136.64 , 136.50 , 124.89 , 122.33 , 122.09 , 121.43 ,

66.54.

1-(Thiophene-2-yl)-N-(thiophene-2-ylmethyl) methanimine. 1H NMR (CDCl3) : δ (ppm)

8.38 (d, J = 1.2 Hz, 1H), 7.38 (dt, J = 5.0, 1.0 Hz, 1H), 7.29 (dd, J = 3.6, 1.1 Hz, 1H), 7.21 (dd,

J = 4.9, 1.5 Hz, 1H), 7.04 (dd, J = 5.0, 3.6 Hz, 1H), 6.99 – 6.92 (m, 2H), 4.92 (s, 2H); 13C NMR

(101 MHz, CDCl3): δ (ppm) = 155.52, 142.19, 141.64, 131.13, 129.44, 127.50, 126.99,

125.38, 124.93, 58.61.

1-Phenyl-N-(1-phenylethyl)ethan-1-imine. 1H NMR (CDCl3) : δ (ppm) 7.99 – 7.91 (m, 2H),

7.59 – 7.49 (m, 1H), 7.45 (ddt, J = 8.2, 6.6, 1.1 Hz, 2H), 7.39 – 7.26 (m, 4H), 7.26 – 7.17 (m,

1H), 4.10 (q, J = 6.6 Hz, 1H), 2.59 (s, 3H), 1.37 (d, J = 6.6 Hz, 3H); 13C NMR (101 MHz,

CDCl3) δ (ppm) =165.03, 137.15, 133.17, 129.48, 128.63, 128.53, 128.43, 128.37, 128.23,

126.87, 126.85, 126.74, 125.75, 59.90, 25.19, 15.66.

N-Heptyl-1-phenylmethanimine. 1H NMR (CDCl3) : δ (ppm) 8.26 (s, 1H), 7.74-7.70 (m,

2H), 7.44 – 7.35 (m, 3H), 3.62-3.58 (m, 2H), 1.72-1.69 (m, 2H), 1.31-1.24 (m, 8H), 0.88 (t, J

= 6.6 Hz, 3H); 13C NMR (101 MHz, CDCl3): δ (ppm) = 160.88, 136.47, 130.59, 128.71,

128.17, 61.97, 31.99, 31.09, 29.30, 27.49, 22.82, 14.28.

S7

3. Supplementary Figures

Figure S1. Optical and fluorescence images of pure NMP, not containing MoS2 nanosheets, as a funciton of heating time (140oC). (a)-(b) under O2 gas, and (c)-(d) under Ar gas.

300 400 500 600

0.00.20.40.60.81.0

Abs

orba

nce

Wavelength (nm)

0 30 60 90 120 180 min

Figure S2. Absorption spectrum of NMP-CDs as a function of reaction time at 140 o

C.

S8

3 nm

0.21 nm

b)a)

50 nm

2 4 6 80

10

20

30

Amou

nt (%

)Size (nm)

292 290 288 286 284 282

Inte

nsity

(cps

)

C=C C-C C-O/C-N C=O O-C=O

C1s

538 536 534 532 530 528

C-O C=O

O1sd)

404 402 400 398

Inte

nsity

(cps

)

Binding Energy (eV)

pyridinic pyrrolic

N1se)

c)

0 200 400 600 800 1000 1200

Binding Energy (eV)

f) WideC1s

N1s

O1s

OKL

L Na

1s

Na

KLL

Figure S3. Characterization of NMP-CDs. (a) TEM image of NMP-CDs (Inset : size

distribution). (b) HR-TEM image of NMP-CDs (Inset : FFT pattern). (c) C1s, (d) N1s, (e)

O1s and (f) wide XPS spectra of NMP-CDs.

S9

10 20 30 40 50 60 70

100

200

300

400

500

600

700

800

Inte

nsity

(a.u

)

2(degree)

MoSHCDs24o (0.37 nm)

Figure S4. XRD spectrum of MoSHCDs.

300 400 500 600 7000.0

0.2

0.4

0.6

0.8

1.0

Norm

aliz

ed In

tens

ity

Wavelength (nm)

Absorption Excitation Emission

Figure S5. Optical properties of NMP-CDs. UV-vis absorption spectrum (black), photoluminescence excitation (PLE) spectrum at an emission of 500 nm (red) and photoluminescence (PL) spectrum of NMP-CDs at an excitation of 400 nm (blue).

S10

2.61 ppm2.80 ppm

N

O

OON

b)

c)

a)

O

OHO

HN

HN O

11.48 ppm-COOH

1.05 ppm0.98 ppm

Aliphatic C-H

Figure S6. (a) 1H-NMR spectra of a MoS2 nanosheets/NMP solution after heating for

3 h at 140oC under O2 atmosphere before purification. (b)-(c) Magnified spectra.

S11

-2 -1 0 1 2

-10

0

10

1.6 eV

Curre

nt (m

A)

Potential vs NHE (eV)

Blank MoSHCD

-1.1 eV

Figure S7. Cyclic voltammogram of MoSHCDs. A Pt disk electrode and silver wire w

ere used as working, counter electrode and quasi-reference electrodes, respectively, in

TBAP solution. Fc was used as a standard and a scan rate was 100mV/s.

450 500 550 600 6500.0

0.2

0.4

0.6

0.8

1.0

Norm

aliz

ed In

tens

ity

Wavelength (nm)

0 mM 58 mM 145mM 290 mM 580 mM

Figure S8. PL response of MoSHCDs to benzylamine at various concentrations (58, 145,

290, and 580 mM).

S12

Figure S9. 1H-NMR spectrum of the reaction mixture for the oxidative coupling of

benzylamine photocatalyzed by MoSHCDs for 12 h at 25oC.

Figure S10. Emission spectrum of a cool white LED lamp.

S13

Figure S11. Emission spectrum of a 300 W Xe lamp.